I think you are over-estimating what an auditor is expected to do. Auditor's, to me, seem to be there to make sure you're compliant with the law or regulation that they are auditing for. In these audits, the company gathers and presents all of the data that the auditors will see.

The auditors will do interviews with people, but the company also (somewhat) picks who will get interviewed.

Remember that auditors are paid for by the company they are auditing. They are motivated to do the minimum required to pass the given regulation. They aren't there for true oversight, they are there to make sure all the checkboxes are checked.